1. Technical Field
The present invention relates to thermal spraying devices that include a means for generating a flame and a means for injecting a powder into the flame. The flame-generating means includes an end piece out of which the flame is directed towards a substrate subjected to spraying. In the context of the present disclosure, the terminology of “thermal spraying device” is used to refer to devices for generating a flame that can be used for the purpose of depositing a coating of metal or ceramic onto a substrate; examples include plasma spray guns of different kinds, flame jet devices, HVOF devices and related arrangements. The technical field of the invention is particularly that of applying coatings, such as thermal barrier coatings of metal or ceramics, onto substrates, and in particular, onto substrates such as constructional elements in aerospace constructions, in particular motor parts thereof. The invention, however, is not restricted to such applications, but instead also can find a number of applications outside this relatively narrow field.
2. Background
Devices for plasma spraying a powder onto a substrate are known that comprise (include, but are not limited to) plasma jet-generating means and one or more powder injection ports via which a powder is injected into the plasma jet. An example of such a plasma jet gun is the widely used F4 Sulzer Metco gun. This product includes an end piece through which the plasma jet is directed out of the gun and towards the substrate that is to be coated. A shoulder or knob is attached to the end piece and is provided with a nozzle that accommodates the injection of powder into the plasma jet.
During operation, when the powder is injected into the plasma jet, melted and deposited onto a substrate, characteristic flow patterns are generated as the powder reaches the jet. Often, during normal operation conditions, a back-stream of powder may return to the nozzle resulting in a clogging of the nozzle. Larger particles of aggregated powder clogged in the nozzle or the end piece will sooner or later come loose and be ejected into the jet. This causes disturbances in the spraying process, resulting in blisters and lumps being generated in the coating.